Monitor Brightness goes up and down by itself

I've recently installed Kubuntu Karmic 9.10 from new. I'm not completely new to Linux, tough.
Couldn't say when this bug started exactly, but it probably came with this latest release.
I own a MSI-Wind netbook and i've previously been using Ubuntu 8.10 and Kubuntu 8.10 & 9.04 and never experienced this trouble.

The problem is the following:
whether i use the fn keys or the slider in the power management settings panel in order to adjust the brightness, it starts going up and down by itself (note that in either case i just press/change it by one step) and never stops.

-> As in previous releases (as well as this does) the gui brightness indicator shows up and indicates correctly the actual brightness strength. It just goes up and down forever. Just to give you an idea, it changes brightness intensity about 10 times per second and never calms down. (The symptom is just as if i got fun pressing madly the up and down fn keys, while i'm effectively pressing them just one time).

The only way i've discovered to stop this madness is to reboot the whole machine.

NOTE: i've discovered that fn keys work right in the pre-grub and grub loading times, and that in that 'short' time i can adjust brightness without having the problem. Once i log in the system i get no chance to press brghtness fn keys once and not experiencing the automatically up&down problem.

What can i do to remedy to this? It must be something simple, i reckon (because in previously releases it worked right).

Tell me what you need and i'll give you :P
Thanks for your future help :D

(PS: i'm italian, but i used english to get to a wider slice of people. So if you're italian too, don't get mad with english and just speak your language if you want.)